Cerebral Cortex

The top layer of the human brain is full of grooves, which significantly enlarge its surface. The brain consists of two symmetrical cerebral hemispheres (also called hemisphere cerebri) that are interconnected by the callus.

The surface is wrinkled, and we can distinguish the brain curves that are separated by furrows. Although both hemispheres are physically identical, they have completely different roles.

The first difference is that they control the opposite sides of the body: the right hemisphere controls the left side of the body, while the left hemisphere controls the right side of the body.

img: Lorenzo Bandieri

The left hemisphere is related to functions of speech, writing, composing sentences, and problem-solving. Also, this half of the left brain is responsible for analytical thinking, while the right hemisphere is responsible for synthesis thinking, by looking at the whole.

At the center of the cerebral hemispheres, the basal ganglia are found. There is a thin but extensive cerebral cortex on the surface of our brain. The basal ganglia play an important role in initiating and controlling movement.

Since space in the skull is very limited, the cerebral cortex is wrinkled, as we have already said, which causes a much larger area of the cerebral cortex to fit into the same volume.

The cerebral cortex is the most developed part of the human brain – four times the size of a gorilla. It is divided into a large number of fields, which differ in the number of layers of neurons and connection with other areas of the brain.

The function of many fields is known – visual, auditory, and sensory, which receives information from the skin (somatosensory cortex) and various motor fields (1). 

The ways that connect the sensory receptors and the cerebral cortex across the centerline. Thus, the cerebral cortex of the left brain controls the right side of the body, and vice versa (1).

Accordingly, sensory signals from the left side of the body go to the right hemisphere, and vice versa. For example, sounds that enter the left ear mostly activate the right cerebral cortex.

However, the two halves of the brain are not isolated one from another – the left and the right cerebral cortices are connected by a large bundle of axons called the callus, corpus callosum. The cerebral cortex is required for voluntary activities, language, speech, and multiple brain functions, such as thinking and memory.

In addition to the neuron bodies, the cortex also contains endings of neurons that reach it from other parts of the brain as well as a rich network of blood vessels. It is thanks to this content that the cortex has a dark gray color.

The largest part of the cortex, as much as 90%, consists of a phylogenetically newer structure – a new cortex, consisting of six layers of stacked nerve cell bodies. The phylogenetically older structure of the cortex consists of the limbic part, which is part of the limbic system and the olfactory zone (1).

Layers of the cerebral cortex

The cerebral cortex contains clearly defined and characteristic brain layers:

  • Lamina molecularis – the surface layer
  • Lamina granularis externa (outer granule) – a well-developed layer in the sensitive region, containing Golgi cells
  • Lamina pyramidalis externa (outer layer of the pyramidal cells) – best developed in the precentral part
  • Lamina granularis internal (inner granular layer) – consists of tiny Golgi cells
  • Lamina pyramidalis internal (inner layer of pyramidal cells, ganglia layer) – in the motor region and it contains large pyramidal Betz cells which is why it was also named “giganto-pyramidalis”
  • Lamina multiformis (polymorphic cell layer) – consists of the spindle cells (1).

Levels of cerebral cortex organization

The cerebral cortex can be divided into three basic levels and functions:

  1. primary
  2. secondary
  3. tertiary cortex

The hierarchically lowest areas are the primary visual, auditory, somatosensory, and motor cortex. The primary sensory cortex receives information through the thalamus.

Primary cortex

The primary cortex receives information from the surrounding environment and the body itself and controls specific muscles. The primary motor cortex corresponds to area 4, i.e. the precentral winding of the frontal lobes.

Pyramidal neurons of this part of the cortex control the movements of individual muscles of the opposite half of the body represented somatotopically in the cortex. This means that each part of the cortex corresponds to a part of the body.

The primary somatosensory cortex is located in postcentral whorls and corresponds to areas 3, 2, and 1. It receives information from the opposite side of the body for touch, pain, temperature, position, and vibration.

The primary visual cortex corresponds to area 17 which surrounds the fissure calcarina (fisura calcarina) of the occipital lobe. Each side receives information from the opposite half of the field of view.

The primary auditory cortex is located on the upper surface of the temporal lobe at the lower edge of the Sylvian furrow and corresponds to Heschl’s transverse gyrus. It receives sounds from both ears.

The primary olfactory cortex is located in the lower posterior lobe of the frontal lobe and insula. It receives all the information of the cortex somatotopically so that each part of the cortex corresponds to a specific part of the visual field, part of the body or internal organs, and the sound frequency.

Secondary cortex areas

The unimodal association cortex is specific to each sense as well as to the motoric system and is in continuity with the primary cortical area.

Tertiary cortex areas

Secondary areas are supplemented by the tertiary areas, that is, the polymodal and supramodal association cortex.

These areas are represented by the parieto-temporal-occipital intersection in the posterior portion of the brain (behind the Roland furrow or the central sulcus) and the prefrontal cortex in the anterior brain.

Functions of the Cerebral Cortex

The frontal lobe is responsible for thinking, planning, performing actions, voluntary movements, speech production, and emotional control. The anterior portion of this lobe is called the prefrontal cortex and it represents the highest part of the CNS.

This is where the highest forms of thought, emotion, and perception of oneself and the social environment take place.

Temporal lobes are involved in the processes of:

  • Hearing (audio observation)
  • Object recognition
  • Memory
  • Feelings
  • Music features.

The parietal lobes house the following centers:

  • The central part of the somatosensory function which consists of cones for touch, pain, temperature, pressure
  • Spatial observations of space and organization of activities in space
  • Centers for processes regarding attention, body language, and some math skills.

The occipital lobes are responsible for:

  • Visual observation
  • Perception of shape, color, movement, and light.

The activities of the cortex are mostly conscious while the activities of the subcortical structures are unconscious.

Cerebral Cortex Damage

Damage to the upper layer of the brain, i.e. it’s surface or the cerebral cortex usually impairs a person’s ability to think, manage emotions, and behave in a regular, usual way (2). As specific areas of the cerebral cortex are generally responsible for specific types of behavior, the type of damage determines the exact location and extent of the injury.

Damage to the front lobe usually affects the patient’s motoric activities. Namely, the frontal lobes of the cerebral cortex are generally guided by the learned and acquired motor skills, such as writing, playing musical instruments, or tying shoes.

These also coordinate facial expressions and expressive movements. Special areas of the frontal lobe are responsible for specific fine motoric activities on the opposite side of the body.

The effects of damage of the frontal lobe on the patient’s behavior vary with the size and location of the physical defect. Small defects usually do not cause noticeable behavioral changes if they affect only one side of the brain, although they sometimes may cause seizures.

Major damage to the back of the frontal lobes can cause apathy, attention disorders, indifference, and sometimes even incontinence.

People with major damage to the forehead or side of the frontal lobes tend to be easily distracted, express inappropriate euphoria, are at times feisty and behave in a vulgar, and rude way. Finally, those patients tend to be reckless and oblivious to the consequences of their behavior (2).

Conclusion

The cerebral cortex (cortex cerebri) is the outer layer of our brain that has a wrinkled appearance. It is divided into fields with specific functions such as sight, hearing, smell, and sensation, and controls higher functions such as speech, thinking, and memory.

The most important part of the brain related to self-development techniques is the anterior cortex, the frontal cortex.

References

  1. Jawabri KH, Sharma S. Physiology, Cerebral Cortex Functions. [Updated 2019 Jun 29]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK538496/  Found online at: https://www.ncbi.nlm.nih.gov/books/NBK538496/
  2. Rubenstein JL. Annual Research Review: Development of the cerebral cortex: implications for neurodevelopmental disorders. J Child Psychol Psychiatry. 2011 Apr;52(4):339-55. doi: 10.1111/j.1469-7610.2010.02307.x. Epub 2010 Aug 24. PMID: 20735793; PMCID: PMC3429600.  Found online at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3429600/